Rack base



FIG. 1 is a top, front, and right side perspective view of a rack base showing our new design;

FIG. 2 is another top, front and right side perspective view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is an enlarged fragmentary top, front and right side perspective view of the right end thereof; and,

FIG. 6 is an enlarged vertical cross-sectional view thereof, taken along line 6—6 of the element shown in FIG. 5.

The broken-line disclosure in the views is understood to represent both environmental structure provided for illustrative purposes only and portions of the rack base which form no part of the claimed design. 

The ornamental design for a rack base, as shown and described. 